Turbomachines such as wind turbines, gas turbines, steam turbines, pumps, fans, generators, motors, and other forms of commercial equipment frequently include shafts, blades, and other rotating components. It is known in the art to install one or more sensors on the rotating components to measure various characteristics of those components in order to control, monitor, and/or enhance the operation of the rotating components. For example, sensors that measure temperature, velocity, stress, strain, vibrations, and/or other characteristics of the rotating components may allow for early detection of abnormalities, adjustments to repair or maintenance schedules, and/or other actions to enhance operations.
Various contact type slip ring systems are known in the art for transmitting the analogue sensor data from the rotating components to stator components for further analysis and/or for transmitting power to or from a rotatable portion of the slip ring assembly. Conventionally, analogue signals from the sensors are routed via transmission lines (i.e. wires) to individual conductive rings of a slip ring assembly. The conductive rings are concentrically positioned along a rotatable center bore or shaft portion of the slip ring assembly. Stationary contact arms or brushes provide a signal path for routing the signals from the conductive rings to a stationary device such as a controller, data processor or the like. The corresponding concentric conductive rings are generally formed with a cross-section shape that may include grooves, slots and/or generally flat or arcuate surfaces that are appropriate for the sliding contact.
In order to accommodate ever increasing data requirements for test and operation of the turbomachine, it is often necessary to transmit high frequency signals such as digitized analogue signals from the sensors to the stationary device via the conductive rings. However, maximum transmission rate across the conductive ring may be limited by various factors.
One potential limiting factor is distortion of the waveforms due to reflections from electrical impedance discontinuities. Impedance discontinuities can occur throughout the slip ring assembly wherever different forms of transmission lines and components interconnect and that have different surge impedances. For example, high-frequency signal losses and/or degradation at the conductive rings may increase with signal frequency due to multiple reflections from impedance mismatches. Some of the highest incidences of impedance mismatches often occur where transmission lines such as a twisted wire pair from the sensors connect at a conductive ring and/or at the brush-conductive ring interface of a slip ring assembly and/or at connector interfaces.
Typically, impedance mismatches may be mitigated by increasing or decreasing the contact surface area (i.e. the width) of the conductive rings that carry high-frequency signals. However, this methodology may limit the number of conductive rings allowed along a given axial length of the center shaft due to limited axial space provided along a center bore of shaft portion of a slip ring assembly. As a result the number of digital transmissions that may be utilized, particularly in cases where overall axial length of the slip ring assembly is at issue, may be limited. Therefore, an apparatus and method for determining axial spacing between conductive rings of a slip ring assembly that provides for constant or substantially constant impedance across the slip ring assembly would be useful.